1. Field of the Invention
The present invention relates to a squeeze pump for continuously transmitting a slurry such as nonhardened concrete containing aggregate.
2. Description of the Related Art
U.S. Pat. No. 4,492,538 was invented by the present inventor. In this squeeze pump, as reillustrated in FIGS. 8 and 9 of the accompanying drawings, a rotary shaft 53 is rotatably mounted centrally in a casing 52 in which a portion of a resilient tube 54 is disposed along an inner periphery of the casing 52 in such a manner that it extends in arc about the rotary shaft 53. Four roller shafts 56 are attached to the rotary shaft 53, and a cyindrical squeeze roller 57 is rotatably mounted on the distal end of each roller shaft 56. Since the squeeze rollers 57 rolls while compressing the resilient tube 54, the slurry in the resilient tube 54 is conveyed in the direction of rolling of the squeeze rollers 57.
However, such squeeze pump has a problem in that when it is operated for a long time, generation of heat would occur at portions where the resilient tube 54 contacts the squeeze rollers 57. It is viewed that this generation of heat results chiefly from frictional heat produced by the slipping between the squeeze rollers 57 and the resilient tube 54. This is because the individual squeeze roller 57 contacts the resilient tube 54 at the same peripheral speed through its entire roller length and hence tends to slip at any of its base, distal end and intermediate portions 57a, 57b, 57c with respect to the resilient tube 54 (FIG.10).
This generation of heat of the resilient tube 54 causes its components, such as rubber and reinforcing yarns, to be deteriorated, thus resulting in a shortened service life of itself.
In order to solve this problem, it is proposed in U.S. Pat. No. 4,492,538 that a taper roller of a diameter increasing gradually toward its distal end is used as each squeeze roller. With such taper squeeze rollers, however, the two roller shafts of each pair of coacting squeeze rollers must be mounted in non-parallel relation to each other, which is difficult.
Further, in the squeeze pump described in U.S. Pat. No. 4,492,538, as shown in FIG. 11, V-shaped valley 154 would be formed in the resilient tube 54 at its portion immediately ahead (upstream of the transmitting direction) of the rolling squeeze rollers 57. If the aggregate (in the slurry) is received in the corner 254 of the valley 154, the aggregate is hard to be advanced past the squeeze rollers 57. Therefore, the aggregate can be caught or jammed in the compressed resilient tube 54, not only damaging the resilient tube 54 soon, but also causing a reduced transmitting efficiency of the slurry. Moreover, the cross-sectional shape of the resilient tube 54, as compressed by the squeeze rollers 57, would vary to be flat, causes a poor transmitting efficiency of the slurry.
Another problem with the squeeze pump described in U.S. Pat. No. 4,492,538 is that the squeeze rollers 57 pull the resilient tube 54 in the direction of revolution when the squeeze rollers 57 leave from the resilient tube 54. Therefore, such pulled portion, which is disposed within the casing 52, of the resilient tube 54 would become entirely smaller in diameter, reducing the transmitting efficiency of the slurry. Further, the resilient tube 54, when thus pulled, would be bent obliquely at its portion which is introduced into the casing 52, and as a result, such bent portion would be broken or damaged soon.
To this end, the present applicant disclosed, in Japanese Patent Laid-Open Publication (Tokkaisho) 58-158389, a squeeze pump such as shown in FIG. 12. In this squeeze pump, a regulating member 55 is mounted in the casing 52 along the arcuate resilient tube 54 for preventing the latter from moving toward the center of the casing 52. However, since the regulating member 55 extends along the entire portion of the resilient tube 54 which is disposed in the casing 52, the squeeze pump is expensive to manufacture.